Fabrication And Study On New Type Ga Doped Based Transparent Conductive Films

Ga doped ZnO (GZO) is one of the most promising transparent conductive oxides for various electronic devices such as solar cells, flat panel display, optoelectronic etc. Magnetron sputtering technique is the most commonly used method to deposit GZO owing to its more advantages such as high deposition rates, process stability and reliability, and preparation of high-quality thin films on large-scale substrates in comparison to the other methods. For application of GZO films to thin film solar cells such as organic solar cell, it is necessary to prepare GZO films at low temperature such as room temperature (RT). However, it is difficult to obtain a film with both low resistivity and high transmittance at RT. In order to improve properties of GZO based transparent conductive thin films, we used different methods and investigated the characteristics of GZO based transparent conductive thin films. The work includes:1. Transparent conductive films of HGZO were deposited on glass under various deposition conditions (ratio of H2 to Ar, RF power, sputtering pressure and time) by RF magnetron sputtering in Ar+H2 ambient at RT. In this work, Taguchi method was used to find optimal deposition conditions and it was found that sputtering time and ratio of H2 to Ar were significantly influencing parameters on figure of merit of HGZO films. For the HGZO film grown under the optimal condition, the highest figure of merit of 33.94×10-3 Ω-1, i.e. the lowest sheet resistance of 10.62 Ω/sq (ρ=3.40×10-4Ωcm) and high transmittance of 90.03% were obtained.2. In order to improve optical characteristics of GZO/Cu film/GZO transparent conductive electrode (TCE), GZO/Cu grid/GZO TCE structures were fabricated at RT by using electron beam evaporation (EBE) for the Cu grids and RF magnetron sputtering for the GZO layers. In this work, we investigated the electrical and optical characteristics of GZO/Cu grid/GZO multilayer electrode for thin film solar cells (TFSCs) to enhance the optical transparency without significantly affecting their conductivity. The calculated values for the transmittance and sheet resistance of the GZO/Cu grid/GZO multilayer were similar to the experimentally observed ones. The highest figure of merit ΦTC is 5.18×10-3Ω-1 for the GZO/Cu grid/GZO multilayer with Cu grid separation distance of 1mm was obtained, in this case, the transmittance and resistivity are 82.72% and 2.17x 10-4 Qcm, respectively.GZO/Cu grid double layer structures were prepared at RT. For the GZO/Cu grid double layer with Cu grid spacing distance of lmm, the highest figure of merit (ΦTC=6.19×10-3 Ω-1) was obtained. In this case, the transmittance, resistivity and filling factor (FF) of GZO/Cu grid double layer are 83.74%, 1.10×10-4 Qcm and 0.173, respectively. The transmittance and resistivity are acceptable for practical TFSCs applications.4. GZO films are deposited on polycarbonate (PC) substrate by direct current (DC) magnetron sputtering at RT. The residual stress of the films is investigated by X-ray difraction (XRD) and wafer curvature method. For the films deposited with the thickness of 225 nm, the film deposited at 140 W has the largest crystal grain and the smallest compressive stress. The result was confirmed by an independent stress measurement method, wafer curvature method. From our experimental results, we suggest that by adjusting the sputtering parameters, such as sputtering power and thickness, the stress relaxation in the GZO thin film grown on polymer substrate at RT could be achieved.